Electric insulator



. April 11, 1939- H. P. SLEEMAN 2,154,387

ELECTRIC INSULATOR Filed May 24, 1938 29(5emi Ccnduedn u -c a 27 {asp-ma: 555;?

l0 INVENTOR MORE/.gsnnm H95 av ms ATTORNEYS."

Patented Apr. 11, 1939 UNITED STATES "PATENT OFFICE f ELECTRIC INSULATOR Harold P. Sleeman, Lisbon, Ohio, assignor to The R. Thomas & Sons Company, Lisbon, Ohio, a corporation of Ohio Application May 24, 1938, Serial No. 209,812 4 Claims. (Cl. 174-140) This invention relates to electric insulators and groove (8 for a line wire conductor, and a cirmore particularly to insulators constructed inja cumferential groove 20 is provided around the manner tending to eliminate interference with head for the reception of a tie wire which secureradio and nearby communication lines, due to ly fastens the line conductor to the insulator in electro-static discharges. conventional fashion. 5

In high voltage electric apparatus electro-static Experience has shown that corona or electrodischarges occur between the metal and the distatic discharges are likely to occur at the folelectric parts of insulators, as between the metal lowing areas of the insulator: In the transverse cap or pin and the porcelain body of some inline conductor groove-as indicated by 22 and sulators, and between the tie wire or cable and 22'; in the circumferential tie wire grooveas in- 10 the dielectric body of other insulators. These dicated by 24; adjacent the periphery of the discharges cause interference with radio recepnesting recess of the upper ,porcelain shell 10- tion and with some communication lines. as indicated by 26; and adjacent the entrance Heretoi'ore various expedients have been emof the supporting pin (not shown) in the lower ll ployed in the manufacture of electric insulators porcelain shell i2 as indicated at". The areas 18 for the purpose of eliminating these electro-static 24, 26, 28 will be understood by those skilled in discharges but these expedients have all had disthe art to be surfaces of revolution, whllethe suradvantages, such as expense of materials and faces 22, 22* include the whole saddle or line coniab rication, diflicult processing, insuil'icient reductor groove. These areas may be generally duction in the amount of discharge and insufliclassed as critical areas for electro-static dis- 20' cient durability. charge or corona.

It is an object of my invention toprovide an I have f und that b pp in a p par tion of improved electric insulator structure which is various metallic oxides to the critical areas of the simple to manufacture and efficient in eliminatunfired clay body of the insulator and then ap-,

ing electro-static discharges. plying the usual non-conducting silicate glaze 25 Another object is to provide, on critical areas 21 ll over the insulator, and then firing the thus of the insulator, a coating having electrical contreated insulator, there is formed between the duction properties and bonded to the porcelain silicate glaze and the porcelain body of the inbody, to reduce to a minimum corona and sur-- sulator a. layer or film 29 of semi-conducting maface discharge efiects at the critical areas. terial. This layer is an ind pend layer t Another object of my. invention is to provide mixed in the la e r n wi h h por elain to a coating of the above type on critical areas 01' any substantia xtent. bu nevertheless.

an electric insulator, which coating shall be probonded to both. Combinations of metal oxides,

tected against abrasion, dust and adverse weathwhich I have used, satisfactorily include those 86 er and other conditions. which have long been used'in pottery and tile Other objects will become apparent as the indecoration, such as manganese, uranium, chrovention is described in the accompanying drawmium, iron and aluminum. ing. In applying the oxide layer, the preparation.

In the drawing Fig. 1 is a side elevation view in the form of a finely ground powder is mixed to 40 of a pin-type insulator with the right half in seca thin consistency with water containing an at- 4 tion, embodying my invention. tachrnent vehicle, such as gum arable and is either Fig. 2 is a side elevation view of a suspension painted, dipped or sprayed on the critical areas or strain-type insulator with the right half in of the unfired clay body prior to the final glazing section, embodying my invention. operation. The glazing is then accomplished Fig. 3 is a fragmentary section view showing usually by immersing the entire insulator into 45 in enlarged detail a portion of the coated area. the liquid silicate glaze. The insulator, when reof the insulator in Fig. 1. v moved from the silicate bath is flredlas usual.

Referring to the drawing, the pin-type insu- Several important advantages attend the lator of Fig. 1 comprises two porcelain shells in anufac u e f ul t with y und a e so and I! having nesting sections with suitably mion uctin layer. placed as indicated.

roughened side walls, as by the attachment 01. Among these advantages are: finely ground porcelain particles ll vitrified to During firing, the glaze protects the oxide the body by means of the surface glaze, and celayer and prevents it from burning away or bemented together by cement ii. The head of ing deleteriously affected, as it would be it not the upper shell is provided with a transverse protected.

After firing and during iise, the glaze protects the under-glaze oxide layer from abrasion, dirt, dust and adverse weather and other conditions. My insulator structure is therefore more durable than other structures provided with heretofore known means of eliminating interference with radio reception.

The under-glaze layeris not accompanied by objectionable discharges occurring at the edge of the layer, such as have occurred when attempts were made heretofore to place conductive coatings of metal on top of the glaze.

Thus the provision of a semi-conducting layer under the glaze according to my invention results in a radio interference-free insulator structure which is more durable, less expensive, and more effective in eliminating electrostatic discharges than any prior structure for similar purpose.

The invention types of insulators. sion or strain-type insulator of Figure 2, may be mentioned. In this type the metal cap 30 is cemented to the porcelain shell or insulator body 32, which has a pin-recess 33 for the insulator supporting pin 34 which is cemented-in the recess. The critical areas in this type of insulator are adjacent the lower edge of the cap 30, as indicated at 35; and adjacent the mouth of the pin recess 33, as indicated at 38. These areas are oxide coated and the insulator is treated in the same manner as described in connection with Fig. 1.

The theory of the invention is not exactly known. Nevertheless, the superior functioning of the under-glaze semi-conducting layer has been demonstrated. Obviously, it was not to be expected that the functions of a layer upon the glaze, in contact with the tie wire and line conductor, or other metal parts, would be performed as well or better by a layer under the glaze. The normal expectation would be that the glaze would insulate the oxide layer from the metal parts and therefore the glaze-covered layer would function in less desirable manner than a metal coating over the glaze. However, due apparently to uneven spreading of the oxide may also be applied to other As an example, the suspenlayer and the glaze, certain minute projections of the oxide through the glare occur. These are or may be engaged by the metal parts or cement in contact with the insulator and thus impart their potential to the whole semi-conducting oxide layer. (In case, however, the glaze should aiford unbroken insulation between the oxide coating and the tie wire, line conductor or other metal parts, a slight abrasive operation to remove a small section of the glaze might be employed.) In absence of certainty, I do not limit my invention to such operation or to the foregoing possible theory.

Many modifications within the scope of my invention will occur to those skilled in the art. Therefore I do not limit the invention to the specific embodiments disclosed.

I claim-- 1. An electric insulator comprising a porcelain body having an area coatedwith a metallic oxide and a silicate glaze over said coated area, said layer and said glaze being afilxed to said porcelain body by firing.

2. The means for eliminating interference with radio reception in a ceramic electric insulator comprising a silicate glaze on said insulator, a semi-conducting layer of material beneath said silicate glaze at predetermined areas, said glaze and said layer being aflixed to said insulator by 3. An electric insulator comprising a porcelain body having an area coated with a mixture of metallic oxides forming a semi-conducting layer of material, a silicate glaze over said coated area, said layer and said glaze being affixed to said porcelain body by firing.

4, In an electric insulator, the means for suppressing electrostatic discharges which tend to interfere with radio reception, comprising a coating of semi-conducting material applied to predetermined areas of the insulator, and a coating of silicate glaze over said coating,'said glaze and coating being affixed to the insulator by firing, a portion of said coating being exposed through said glaze in position to contact with metal parts attached to said insulator.

HAROLD P. SIEEMAN. 

